In most cars and trucks, the driver sits behind a steering wheel that he or she grasps and turns to steer the vehicle. For favorable customer perception of a new vehicle, it is considered desirable that the steering wheel appear symmetric to the driver when the steering wheel is steering the vehicle in a straight line. In a steering system that is fully functional, a steering wheel that appears noticeably asymmetric when the vehicle is being steered in a straight line may incorrectly suggest a problem, or perhaps even a defect, to the driver or prospective purchaser, and at a minimum may create the impression of poor manufacturing quality. Extreme asymmetry may cause a condition that impairs driver visibility of instrument panel gauges and/or controls.
Asymmetry may also result from the manner in which a particular vehicle is being driven on a particular road surface. This is perhaps more true of large commercial vehicles like heavy trucks than of smaller passenger vehicles. Unevenly distributed cargo loads, the mass of a particular commercial truck or trailer body, and crown roadways are among potential causes for an asymmetric appearance of the steering wheel when a vehicle is being driven in a straight line on a road surface.
When a condition of asymmetry is deemed to need correction, a typical procedure is to disconnect the steering wheel from the steering shaft, re-position it on the shaft, and then re-connect it to the shaft.
The ability to make exactly the needed correction is problematic in a steering system where the steering wheel and steering shaft are connected to each other through a spline connection. Such a connection has a finite number of splines repeating at a defined angular interval. That fact presents only a finite number of possibilities for locating the wheel to the shaft.
If a typical angular spline interval is 4°, the resolution to which a splined steering wheel can be circumferentially registered with a splined steering shaft is the same. That constraint leaves the possibility that a steering wheel installed in a new vehicle in accordance with proper assembly procedures may present the appearance of having up to 2° of asymmetry in either clockwise or counterclockwise direction when steering the vehicle in a straight line.
Furthermore, correction of asymmetry by disconnecting the steering wheel from the steering shaft and then re-connecting it to the shaft creates the potential for mistake if due care is not exercised. A service technician or other individual performing the correction must comply with specified procedures that are developed by manufacturers at significant expense. When a manufacturer has no control over such person and cannot monitor the work being performed, a serious mistake resulting from the inability of the manufacturer to supervise technician repair may adversely impact the manufacturer even though the manufacturer is not at fault in any way. For trucks equipped with steering wheel air bags, OEM's and air bag suppliers recommend that only qualified licensed mechanics remove and install them because of the risk that static electricity or careless handing might cause their deployment if they are not handled in accordance with OEM/supplier installation/removal instructions. An untrained driver of such a truck seeking to adjust the steering wheel by removing it and re-positioning it, risks accidental air bag deployment in doing so.
And regardless of the above considerations, the time, tools, and effort needed to correct steering wheel asymmetry are significant. Moreover, they may be a source of warranty claims, even repeat claims, in vehicles under warranty.